Field of the Invention
The present invention relates to an image forming apparatus for forming an image having a high degree of image quality.
Description of the Related Art
Conventionally, there have been proposed image forming apparatuses based on various kinds of principles, which are used as output terminals of personal computers, workstations or the like. In particular, color electrophotographing apparatuses utilizing the electrophotography and the laser scanning technology are advantageous in view of its high recording speed and high printing quality, and have been used prosperously as color printers.
In the image forming apparatus of this kind, latent images formed on a photoreceptor belt are successively manifested with the use of developing means so as to form different color toner images which are then transferred from the photoreceptor belt onto an intermediate transfer medium and are synthesized into a color image medium, and the thus obtained color image is transferred in batch onto a paper sheet. Further, as to the developing means, developing means of a one-component developing type have been prosperously used since it is small-sized, inexpensive, reliable and so forth.
Next brief explanation will be made of the one component developing means with reference to FIG. 7.
Referring to FIG. 7, toner 2 is reserved in a toner chamber 1a defined in the upper part of a developing tank 1. A pair of toner supply rollers 3a for feeding the toner from the toner chamber 1 onto the downstream side thereof are arranged in the lower part of the toner chamber 1, being opposed at their peripheral surfaces to each other so as to be rotated in opposite directions. A toner agitating member 3b for preventing congregation of the toner 2 and conveying the same onto the downstream side thereof is provided below the toner supply roller 3a.
Below the toner agitating member 3b, there is arranged a toner supply roller 3c for supplying the toner 2 which has been conveyed by the agitating member 3b, onto a developing roller 3d. The toner supply roller 3c is composed of a metal core and a conductive foamed urethane sponge layer bonded to the core metal. The developing roller 3d which is made into contact with the outer peripheral surface of the toner supply roller 3c carries thereon the toner 2 transferred from the toner supply roller 3c, for manifesting a latent image formed on a photoreceptor belt (which is not shown) by using the toner 2. The developing roller 3d is composed of a metal core and a conductive silicone rubber layer in the form of a roll, covering the outer peripheral surface of the metal core, and is adapted to be rotated in the same direction as that of the toner supply roller 3c. Further, it is noted that the toner supply roller 3c and the developing roller 3d are rotatably supported at their opposite ends to the developing tank 3.
A developing blade 4 is provided, abutting against the developing roller 3. This developing blade 4 is composed of a leaf spring member made of stainless steel, phosphor bronze or the like, and an urethane rubber element integrally incorporated with the leaf spring member at one end of the latter, and two rigid metal plates clamping therebetween the other end of the leaf spring member. With this structure, the metal blade 4 is made into contact with the developing roller 3d, for forming the toner 2 in a uniformly thin layer on the developing roller 3d, and for charging the toner 2.
It is noted here that electrophotographing apparatuses are in general sensitive to environmental variation and variation with time (aging effect) so as to change its input/output characteristics of latent image forming process and developing process and the like, and accordingly the quantity of toner sticking to an image bearing medium, for manifesting a latent image given by the same image data varies so as to cause the image quality of the image to be inferior. In particular, in a color image, there has been raised such a problem that the color reproducibility for synthesizing a plurality of toner colors is low.
Accordingly, there has been proposed, as a countermeasure for preventing occurrence of the above-mentioned image quality deterioration, a density compensating technology such that a plurality of test patches (toner images) having different toner densities are formed on the photosensitive belt or the intermediate transfer medium, as shown in FIG. 8, and the densities of the toner images are detected by a density sensor in order to use the results of the detection for compensating process conditions in a latent image forming process or a developing process.
However, through the provision of the above-mentioned conventional test patches, unused toner on the developing roller passes by the developing blade by several times, and accordingly, the charged value of the toner is increased so that the densities of the images are lowered, resulting in decreased densities and uneven densities in the test patches in the vicinity of the leading end thereof, as shown in FIG. 9. Further, since the density is controlled, being based upon such inferior test patches, the accuracy of the density control itself is also deteriorated, causing deterioration of image quality.
The decrease in the densities of the test patches in the vicinity of the leading end thereof, is caused by such a fact that all toner on the developing roller passes by the developing blade by several times so that the charged value of the toner is increased. Further, the unevenness in density within the test patches, is caused by such a fact that additional toner is applied to a part which is developed as a test patch so as to result in occurrence of difference in charged value between the toner in the part and toner in a part which has not yet been developed (The charged value of the toner in the part having not yet developed is higher than that of the toner having additionally been fed since the former passes by the developing blade by a number of times which is greater than that of the latter).